The electro-optic identification (EOID) sensor is used in underwater vehicles for remote identification of proud (i.e., standing clear on the sea bottom), partially buried, and moored mines in the shallow water and very shallow water regions. EOID sensing is based upon laser line scan (LLS) technology that produces images by synchronously scanning a narrow beam and a narrow field-of-view (FOV) receiver across the sea bottom. In general, LLS technology reduces the detrimental effects of backscatter and blur/glow/forward scatter to produce underwater images of excellent resolution, contrast and range. However, since identification algorithms for EOID data are beyond current technology, mine identification is conducted by manual inspection of EOID imagery as data is collected. Consequently, electro-optic image enhancement techniques are needed to improve EOID image quality so that mines can be reliably and more easily distinguished from associated clutter especially in turbid coastal water conditions.
Furthermore, laser line scan imagery can have fluctuating brightness or contrast regions due to high/low signal strength variations when scanning data. High signal strength regions occur when the EOID sensor is perpendicular to a reflective surface (i.e., sea bottom) where photons travel the shortest distance resulting in less scattering effects. Low signal strength regions occur at off-angle scan-lines and sudden drops of elevations in the reflective surfaces where photons must travel further resulting in more scattering effects. The low signal strength regions can obscure visibility of image details thereby allowing objects to "hide" within image shadows.
One image enhancement technique used to enhance high/low signal strength regions is disclosed in the above-referenced co-pending patent application entitled "Background Equalization for Laser Line Scan Data." However, this technique is not capable of operating as an automated image enhancement process because parameters used by the process are sensitive to the environmental conditions of the image and must be supplied by user interaction. Also, the background equalization routine sometimes introduces a smudge effect with high contrast objects. While these high contrast objects are still visible after enhancement, the smudge effect is aesthetically displeasing and can slightly alter the original geometric shape of the imaged object.